The present invention relates to a process for printing disperse dyes onto glass or ceramic surfaces, and more particularly to such a process which yields improved results from the standpoint of dye fastness and pattern flexibility.
Previously, the conventional technique for painting or decorating non-metallic, inorganic surfaces such as glass or ceramic surfaces was by screen printing. In a typical screen printing operation, a separate screen is made for each color to be applied. A first screen is brought into registry with the glass or ceramic surface and a first color painted thereon. A second, third, and fourth screen, if necessary, each representing different colors, is then brought into registry with the glass or ceramic surface and the additional colors painted or brushed thereon through the pattern in the screen. There are many disadvantages to such screen printing techniques. Each color must be applied individually, dried, and cured before the next color can be applied. Thus the time and cost factors become high. Secondly, it is difficult to register the plurality of screens in exactly the right position so that the colors do not overlap. As a result the waste factor may become enormous. The paints or dyes utilized in conjunction with screen printing are not transparent. Further half-tones cannot be achieved by screen printing and therefore true replicas of patterns or scenes are not possible.
In the textile industry, the problems associated with screen printing have been overcome, to some extent, by a process known as "heat-transfer printing" in which a carrier consisting usually of paper or aluminum foil is printed with sublimable dyes and temporarily affixed to the carrier by the use of binders. The carrier so printed is then laid with the printed side adjacent the fabrics to be printed, and is then heated under pressure to a temperature in the range of 160.degree. to 220.degree. C. on the unprinted side of the carrier to sublime the dyes onto the fabric.
The heat-transfer printing technique has been attempted on a wide variety of sheet-like articles such as wood, metals, glass, ceramics, and certain synthetic resins by providing such articles with a surface layer or coating of a thermoplastic resin which presumably adheres to the surface of the substrate and accepts the sublimable dyes. See German patent application DOS No. 2,642,350; French Pat. No. 2,230,794; and British Pat. No. 1,517,832. Similarly the surface of the article to be printed may be coated with a thermosetting resin (published European patent application No. 14,901) which receives the dyes. Characteristic of all of the above approaches is that the transfer of the dyes by sublimation onto the thermosetting or thermoplastic resin is effected by means of heat supplied or generated by an external source.
While the above described techniques temporarily result in a somewhat satisfactory product with the dyes affixed to the resinous layer, which in turn is deposited on the glass or ceramic surface, serious problems have been observed. First of all, the thermosetting and/or thermoplastic resin tends to release from nonmetallic, inorganic surfaces such as glass or ceramic in the presence of moisture such as would be present during washing, in bathrooms, or on items subjected to the outside elements. As the resinous coating peels away from the glass or ceramic surface, the decorative pattern vanishes. Further, disperse dyes tend to fade when subjected to sunlight. Also when the disperse dyes are applied to a resinous coating on glass or ceramic surfaces, a strange phenomenon is discovered in that the disperse dyes oxidize after a short period of time. When oxidized, the surface becomes distorted and a large percentage of the inks rise to the surface and spread. The inks can be readily wiped off and the decorative pattern is lost.
A glass or ceramic surface, on the other hand, when treated with the disperse dyes would be highly desirable if the problems discussed hereinabove could be overcome. Disperse dyes, as opposed to screen printing inks are transparent and give rise to various additional uses and unique aesthetic effects. Some examples of products resulting from disperse dyes utilized to decorate glass surfaces include mirrors with transparent images or decorations thereon; mirrors with frosted images; simulated stained glass windows; mirrors with a printed image between the glass and silver; glass which is printed on the reverse surface and frosted; and shower doors which could be treated with any number of decorative patterns not now available.
According to the present invention there is first provided a technique for printing and permanently affixing disperse dyes onto a glass or ceramic surface in such a manner that the printed pattern is transparent and withstands moisture. This is accomplished by treating the glass or ceramic surface with a silane primer coat which bites into and bonds to the glass or ceramic surface. When a clear thermoplastic or thermosetting resin is applied to the glass or ceramic surface either subsequent to or along with the silane primer, the resinous coating becomes bonded tightly to the glass or ceramic surface and resists peeling even in the presence of moisture. While most thermoplastic and thermosetting resins will provide acceptable results, the aliphatic urethanes, notably polyurethane, appear to be the preferred organic polymeric resins.
The transfer paper or foil with the disperse dyes affixed thereto according to conventional techniques is brought into contact with the glass or ceramic surface and heated (375.degree. F. to 420.degree. F.) under pressure from the reverse side to transfer the printed pattern onto the organic polymeric resin.
As noted hereinabove after a short period of time (less than 30 days) the disperse dyes begin to oxidize and the pattern lost or distorted if not treated with some type of protective coating. Therefore, a sealer composition, which may be either lacquer, varnish, or clear polymeric resins is applied to the printed pattern shortly (within 30 days) of the time the pattern is first printed onto the glass or ceramic surface to prevent the oxidation thereof.
Since the disperse dyes tend to fade in the presence of ultraviolet light, as from sunlight, in order to fix the dyes and prevent fading, there is provided an ultraviolet absorber either in the polymeric resin or in the sealant or in both.
A further, completely different decorative effect can be achieved by frosting the print pattern. Frosting is accomplished by mixing a flatting agent in the aforesaid sealer composition. Flatting agents are substances (such as silica) ground into minute particles, powders, or irregular shapes to disperse incident light rays so that a dull matte or non-glossy effect is produced. When mixed with the sealant a frost produces a unique and novel appearance in which the printed colored area of the glass or ceramic shows through the frosted portion.
It is therefore an object of the present invention to provide an improved process for printing and affixing non-metallic, inorganic surfaces such as glass or ceramic with disperse dyes.
It is another object of the present invention to provide a process of the type described by treating the glass or ceramic surface with a bite chemical which causes the organic polymeric resin upon which the disperse dyes are deposited to firmly and permanently adhere to the glass or ceramic surface even in the presence of moisture.
It is yet another object of the present invention to provide a process of the type described in which the colors do not fade.
Another object of the present invention is to provide a process of the type described in which the disperse dyes do not oxidize.
Yet another object of the present invention is to provide a process for applying a frosted disperse dye finish to a glass or ceramic surface by the use of a flatting agent.